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soc:2010:cooldavid:journal:week2 [2010/05/29 02:09] cooldavid |
soc:2010:cooldavid:journal:week2 [2010/06/04 05:47] (current) cooldavid |
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| - | === Week 2: Discuss TCP and memory changes, update jme driver === | + | ==== Week 2 [ 31 May - 6 Jun 2010 ]: Discuss TCP and memory changes, update jme driver ==== |
| - | == TCP / memory topic == | + | ==== jme driver ==== |
| - | * Current heap size is fixed at 128K. | + | |
| - | * Although it only uses 128K, all-drivers image already overlapped with heap address. | + | |
| - | * Trying to figure out a way to obtain more memory, and report it to OS. | + | |
| - | * See if it is possiable to know how much heap size we can use out of code and stack. | + | |
| - | + | ||
| - | == jme driver == | + | |
| * From Joshua Oreman | * From Joshua Oreman | ||
| * jme_check_link(struct net_device *netdev, int testonly)\\ | * jme_check_link(struct net_device *netdev, int testonly)\\ | ||
| * In this function, I believe the code and string data used in constructing linkmsg will make it into even non-debug versions of the executable. If that's true it would be better if you could perform all the manipulations in the final DBG() line, using the ?: operator and such. It's possible the compiler is clever enough to know what strcat() does and see that linkmsg[] is not used in non-debug, though, so this may be moot. | * In this function, I believe the code and string data used in constructing linkmsg will make it into even non-debug versions of the executable. If that's true it would be better if you could perform all the manipulations in the final DBG() line, using the ?: operator and such. It's possible the compiler is clever enough to know what strcat() does and see that linkmsg[] is not used in non-debug, though, so this may be moot. | ||
| * From Michael Brown | * From Michael Brown | ||
| - | * if (memcmp(addr, netdev->hw_addr, ETH_ALEN)) { | + | * if (memcmp(addr, netdev->hw_addr, ETH_ALEN)) |
| * No need for this compare; just always write the MAC address. (This code will fail if you set the MAC to a non-default value, then try to set it back.) | * No need for this compare; just always write the MAC address. (This code will fail if you set the MAC to a non-default value, then try to set it back.) | ||
| + | * Code cleanups | ||
| + | * gPXE dose not use any DMA address that is above 4G <code C> | ||
| + | #if __x86_64__ | ||
| + | rxdesc->desc1.flags = RXFLAG_64BIT; | ||
| + | #endif | ||
| + | </code> | ||
| + | * Use struct ethhdr and eth_ntoa(). | ||
| + | * Drivers should generally not try to parse the packets they transmit and receive. | ||
| + | * This code will break if/when software VLAN support is added. <code C> | ||
| + | DBG2("Received packet: " | ||
| + | "from %02x:%02x:%02x:%02x:%02x:%02x " | ||
| + | "to %02x:%02x:%02x:%02x:%02x:%02x " | ||
| + | "type %04x\n", | ||
| + | *(uint8_t *)(rxbi->data + 6), | ||
| + | *(uint8_t *)(rxbi->data + 7), | ||
| + | *(uint8_t *)(rxbi->data + 8), | ||
| + | *(uint8_t *)(rxbi->data + 9), | ||
| + | *(uint8_t *)(rxbi->data + 10), | ||
| + | *(uint8_t *)(rxbi->data + 11), | ||
| + | *(uint8_t *)(rxbi->data + 0), | ||
| + | *(uint8_t *)(rxbi->data + 1), | ||
| + | *(uint8_t *)(rxbi->data + 2), | ||
| + | *(uint8_t *)(rxbi->data + 3), | ||
| + | *(uint8_t *)(rxbi->data + 4), | ||
| + | *(uint8_t *)(rxbi->data + 5), | ||
| + | be16_to_cpu(*(uint16_t *)(rxbi->data + 12))); | ||
| + | </code> | ||
| + | * %p should be used for printing out pointer values. <code C> | ||
| + | DBG2("TX buffer address: %08lx(%08lx+%x)\n", | ||
| + | (unsigned long)iob->data, mapping, len); | ||
| + | </code> | ||
| + | * This will behave poorly when memory runs out. Better is to have a refill routine that runs after the poll(), and always attempts to refill up to a specified level. <code C> | ||
| + | rxdesc += idx; | ||
| + | if (jme_make_new_rx_buf(rxring->bufinf + idx)) { | ||
| + | DBG("Dropped packet due to memory allocation error.\n"); | ||
| + | netdev_rx_err(netdev, NULL, -ENOMEM); | ||
| + | } else { | ||
| + | </code> | ||
| + | |||
| + | * From me: | ||
| + | * The refill function did not work correctly. Because of the error packet was reused instead of making a hole. [[http://bbs.cooldavid.org/git/?p=gpxe.git;a=commitdiff;h=aa105ed1c6d99588dceeec3ead4e434b40b59644|This patch fixed it]] | ||
| + | |||
| + | ==== Trace memory related codes ==== | ||
| + | * Current heap size is fixed at 128K. | ||
| + | * Trying to figure out a way to obtain more memory, and report it to OS. | ||
| + | * See if it is possiable to know how much heap size we can use out of code and stack. | ||
| + | |||
| + | === Schedule for memory and TCP modifications === | ||
| + | - Trace how the gPXE boot, relocate, and fill segment informations. | ||
| + | - Try to understand how Michael Brown removes the even magabyte limit. | ||
| + | - Start a discussion on the list about how to reasonably extend gPXE's usable memory. | ||
| + | - Patch gPXE to support large(Several MB perhaps) heap memory. | ||
| + | - Design/discuss a TCP receive window advertisement algorithm. | ||
| + | - Patch gPXE with ''**TCP receive queue**'', ''**SACK Support**'', and ''**Window scale**''. | ||
| + | - Do some benchmark against different window size, and different network environment. | ||
| + | - Post the result and discuss it on the gpxe mailling-list. | ||
| + | |||
| + | === Some notes after trace === | ||
| + | * [[soc:2010:cooldavid:notes:gpxememlayout|gPXE memory layout]] | ||
| + | * Good articals for understanding Gate-A20 | ||
| + | - [[http://en.wikipedia.org/wiki/A20_line|WIKIPEDIA - A20 line]] | ||
| + | - [[http://www.win.tue.nl/~aeb/linux/kbd/A20.html|A20 - a pain from the past]] | ||
| + | === Expand heap === | ||
| + | * [[soc:2010:cooldavid:notes:expandheap|Expand gPXE heap]] | ||
